Voltage regulation system comprising operating condition detection means

ABSTRACT

The invention relates to a system for generating an output voltage (Vout) from an input voltage (Vup), said system comprising:—regulation means (T 1 ) for regulating said output voltage (Vout) to a target voltage level (Vcons), said regulation means (T 1 ) comprising a control terminal intended to receive a regulation signal (SR) and an output terminal for delivering said output voltage (Vout),—first control means (COMP 1 ) for delivering a first control signal (SC 1 ) from a comparison between said regulation signal (SR) and a first reference signal (Vref 1 ).

FIELD OF THE INVENTION

The invention relates to a system for generating an output voltage froman input voltage.

The invention has a number of applications in appliances using smartcards.

BACKGROUND OF THE INVENTION

In order to exchange data in a unidirectional or bidirectional manner,the smart cards require a regulated voltage supply Vout capable ofdelivering a certain current Iout, from an input voltage Vup. Thissupply, for which an embodiment is described in the FIG. 1, is generallydelivered by an interface circuit contained in a smart-card reader.

The voltage supply which is delivered to the smart card is a stabilizedsupply whose output level is regulated to a certain value compatiblewith the characteristics of the smart card. In general, this regulationof the voltage allows to guarantee an output voltage equal to a targetvoltage Vcons, with a margin or error of a few percent.

In parallel, the supply to the interface circuit comprises control meansto generate a change of state of a second control signal SC2 when thecurrent flowing in the smart card exceeds a certain threshold value, forexample to forewarn a possible short-circuiting in the smart card.

However, this interface circuit has functional limitations.

In normal operating conditions, the input voltage Vup must remaingreater than the target voltage Vcons so that the regulation of thevoltage is done correctly, and therefore a correct supply to the smartcards is guaranteed. If for any reason, the input voltage Vup just dropsbelow the target voltage Vcons, then the output voltage Vout also dropswithout any control signal being generated. As this drop in voltage isnot detected, it can be detrimental to the operation of the smart cardor for the application using the smart card.

On the other hand, in case of a large drop of the input voltage Vup, theoutput current Iout which is flowing in the smart card is no longersignificant as the smart card is no longer supplied by the correctoutput voltage Vout. The control means which generate the second controlsignal SC2 can then no longer play their role. If a short-circuit in thesmart card occurs at this moment, the short-circuit has the risk of notbeing detected and runs the risk of deteriorating the application usingthe smart card.

OBJECT AND SUMMARY OF THE INVENTION

It is an object of the present invention to propose a system forgenerating a regulated output voltage Vout from an input voltage Vup andwhich makes an improved detection possible of the operating conditionsof the voltage regulation.

For this purpose, the system according to the invention comprises:

-   -   regulation means T1 for regulating said output voltage Vout to a        target voltage level Vcons, said regulation means T1 comprising        a control terminal intended to receive a regulation signal SR        and an output terminal for delivering said output voltage Vout,    -   first control means COMP1 for delivering a first control signal        SC1 from a comparison between said regulation signal SR and a        first reference signal Vref1.

By directly comparing the regulation signal SR to the first referencesignal Vref1, a control signal SC1 is generated as soon as the voltageregulation done by the regulation means T1 becomes impossible. The firstcontrol signal SC1 therefore adopts an initial state when the regulationconditions are correct and a second state when the operating conditionsfor the regulation are no longer satisfied, in particular, when theinput voltage Vup drops by a large amount with respect to the targetvoltage Vcons.

The detection of the operating conditions of the voltage regulation isonly parametered by the value of the first reference signal Vref1. Sucha system is therefore only dependent on the input voltage threshold Vup,and independent of the amplitude variations of Vup, which facilitatesthe regulation and the setting.

According to an additional characteristic, the system according to theinvention has second control means COMP2 for delivering a second controlsignal SC2 from a comparison between a fraction Ik of the current Ioutdelivered by said regulation method T1 on said output terminal and asecond reference signal Vref2.

This allows to generate a second control signal SC2 which indicates theoperating conditions with regard to the value of the current Ioutdelivered by the voltage supply. The second control signal SC2 thereforeadopts a first state when the output current Iout delivered by thevoltage supply is of nominal value and a second state when the outputcurrent Iout exceeds a certain threshold depending upon the secondreference signal Vref2.

The generation of the control signals SC1 and SC2 being independent ofeach other, an exceeding of the value of the output current Iout can bedetected at the same time as a drop in the input voltage Vup occurs.

According to an additional characteristic, the system according to theinvention comprises means P1-P2-T5 for deactivating the generation ofsaid output voltage from said first control signal SC1 or said secondcontrol signal SC2.

Considering that a change of state of the control signals SC1 and SC2characterizes the beginning of an abnormal operation of the system, thatis, a very high drop of the input voltage Vup or a too high outputcurrent Iout, the control signals SC1 and SC2 are advantageously used todeactivate the generation of the output voltage Vout supplied to thesmart card. This limits the risk of damage to the smart card and theapplication using the smart card.

The invention also relates to an interface circuit comprising a systemaccording to the invention as described above for generating an outputvoltage Vout at a smart card, and a smart card reader comprising such aninterface circuit.

The invention also relates to an integrated circuit comprising a systemaccording to the invention as described above for generating an outputvoltage Vout from an input voltage Vup.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be further described with reference to examples ofembodiments shown in the drawings to which, however, the invention isnot restricted. In the drawings:

FIG. 1 describes a system for generating an output voltage Vout from aninput voltage Vup and which allows to deliver a second control signalSC2 indicating an exceeding of the output current Iout,

FIG. 2 describes a system according to the invention for generating anoutput voltage Vout from an input voltage Vup, and which allows todeliver a second control signal SC2 indicating an exceeding of theoutput current Iout, and a first control signal SC1 indicating a drop inthe input voltage Vup,

FIG. 3 describes a system according to the invention, which de-activatesthe generation of the output voltage Vout from the first and/or secondcontrol signals SC1-SC2,

FIG. 4 illustrates temporal variations of the output voltage Vout as afunction of the various control signals generated by the systemaccording to the invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 describes a system for generating an output voltage Vout from aninput voltage Vup, and which allows to deliver a second control signalSC2 indicating an exceeding of the output current Iout. The outputvoltage Vout is in particular intended to supply a smart card (notshown).

The system comprises regulation means for regulating the output voltageVout to a reference value given by a target signal Vcons. Depending uponthe type of smart card used, the target signal Vcons can be fixed at 5V,3V or 1.8V, with a maximum current Iout of 60 mA, 60 mA or 30 mArespectively.

The regulation means comprise a transistor T1, for example a MOStransistor, the transistor Ti having a gate defining a control terminalintended to receive a regulation signal SR, a drain defining an outputterminal intended to deliver said output voltage Vout, and a sourceconnected to the input voltage Vup. The regulation signal SR isgenerated by a control device CONT having two inputs for receiving, onthe one hand, the output voltage Vout to be regulated and, on the otherhand, the target signal Vcons. The control device thus generates aregulation signal SR corresponding to an error between the two inputsignals Vout and Vcons. For this purpose, the control device CONTcomprises connected in series, a comparator COMP having two inputs andan low-pass output filter F guaranteeing the stability of the regulationloop formed by the elements T1-CONT. Such a regulation loop is known toa skilled person. When the output voltage Vout tends to be lower orhigher than the set signal Vcons, the regulation signal SR varies insuch manner as to bring back the output voltage Vout to the target valueof the signal Vcons, by modifying the polarisation of the transistor T1on its control terminal.

The system also comprises second control means COMP2 for delivering asecond control signal SC2. The control means COMP2 perform a comparisonbetween a fraction Ik of the current Iout delivered by the regulationmeans T1 on said output terminal to the smart card and a secondreference signal Vref2. The second control means COMP2 correspond, forexample, to a comparator with two inputs. The object of the secondcontrol signal SC2 is to indicate an abnormal exceeding of the outputcurrent Iout delivered to the smart card.

The fraction Ik of the current Iout is obtained by using a currentmirror of the type known to the skilled person. The current mirrorcomprises the transistor T2 receiving at its gate the regulation signalSR, the transistors T3 and T4, and the resistance R2 connected to avoltage source VDD. The current mirror allows to deliver in theresistance R2 a current Ik satisfying the relation Ik=Iout/K, where K isthe reduction factor determined by the characteristics of thetransistors T2-T3-T4.

The second reference signal Vref2 corresponds to the node potentialbetween a current source S and the resistance R1, the current source Sgiving a reference current Iref to the resistance R1 connected to thevoltage source VDD.

The second control signal SC2 therefore adopts a first state when thecurrent Iout delivered by the supply is lower than the threshold valuedefined by the relation (K*Iref*R1/R2), and a second state when thecurrent Iout delivered by the supply is higher than said thresholdvalue.

FIG. 2 describes a system according to the invention for generating anoutput voltage Vout from an input voltage Vup and which allows todeliver a second control signal SC2 indicating an exceeding of theoutput current Iout, and a first control signal SC1 indicating a drop ofthe input voltage Vup below a certain threshold.

In addition to the elements described in the FIG. 1, the systemdescribed in the FIG. 2 comprises first control means COMP1 fordelivering a first control signal SC1. The first control means COMP1perform a comparison between said regulation signal SR and a firstreference signal Vref1. The first control means COMP1 correspond forexample to a comparator with two inputs.

By directly comparing the regulation signal SR to the first referencesignal Vref1, a first control signal SC1 is generated as soon as thevoltage regulation executed by the regulation means becomes impossible,ie. when the input voltage Vup drops too much compared to the targetsignal Vcons.

When the input voltage Vup drops too much compared to the target voltageVcons, even a regulation signal SR of a level close to a zero levelrendering the MOS transistor T1 equivalent to a closed switch, it is notsufficient to obtain an output voltage Vout close to the target signalVcons.

The drop of the input voltage Vup is therefore detected by fixing thefirst reference signal Vref1 at a value close to zero, for example 200mV. In this manner, the first control signal SC1 adopts a first statewhen the regulation conditions are correct, ie. when the regulationsignal SR is higher than Vref1, and the first control signal SC1 adoptsa second state when the operating conditions of the regulation are nolonger satisfactory, i.e. when the regulation signal SR is lower thanVref1.

The change of state of the first control signal SC1 therefore permitsthe detection of the malfunctioning of the regulation of the outputvoltage Vout.

The info contained in the first and second control signals SC1 and SC2can thus be used advantageously to activate certain means at theapplication level, or thus inform the application using the smart card(for example the smart card reader) of the detection of a malfunctioningin the supply system to the smart card.

FIG. 3 describes a system according to the invention which permits thede-activation of the generation of the output voltage Vout from saidfirst and second control signals SC1 and SC2.

In addition to the elements described in the FIG. 2, the systemcomprises a logic OR-gate P1 having two inputs and being intended toreceive the first and second control signals SC1 and SC2, for generatingan output control signal SC. The output control signal SC thereforeindicates both a drop of the input voltage Vup and/or an exceeding ofthe output current Iout. This output control signal SC can be used toinform the application—for example the smart card reader—of amalfunctioning in the supply to the smart card. The signal SC can alsobe used to deactivate the generation of the output voltage Vout when atoo important drop of the input voltage Vup occurs, or when the outputcurrent Iout is exceeded. For this purpose, the system comprises a logicgate P2 of the inverter type to reverse the output control signal SC,the output signal of the inverter P2 being connected to the gate of aMOS transistor T5. In addition, the transistor T5 has its sourceconnected to the input voltage Vup and its drain connected to the gateof the transistors T1 and T2. Depending upon the level of the outputcontrol signal SC, the transistor is either equal to an opened switch orto a closed switch. When the transistor T5 is equal to an opened switch,it applies a bias voltage to the gates of the transistors T1 and T2 sothat the regulated output voltage Vout is normally generated at thesmart card. When the transistor T5 is equal to a closed switch, itapplies a bias voltage to the gate of the transistors T1 and T2 so as todeactivate the generation of the output voltage Vout at the smart card.

FIG. 4 illustrates the temporal variations of the output voltage Vout asa function of the various first and second control signals SC1 and SC2generated by the system according to the invention.

Up to the instant t0, the input voltage Vup is higher than the targetsignal Vcons, so that, the voltage regulation can be carried outcorrectly. No exceeding of the output current Iout occurs. The first andsecond control signals SC1 and SC2 have the low logic level. The outputvoltage Vout is therefore regulated to the target signal level Vcons.

Between the instants t0 and t1, the input voltage Vup becomes lower thanthe target signal Vcons, so that, the voltage regulation can no longerbe carried out correctly. This voltage drop is detected by means of thefirst control means COMP1 which then delivers a first control signal SC1at a high logic level. The output control signal SC also moves to thehigh logic level, which closes the switch formed by the transistor T5.The output voltage Vout is then deactivated and its level moves to zero.The second control signal SC2 remains at the low logic level becauseduring this period the current Iout has not been exceeded.

Between the instants t1 and t2, the input voltage Vup once again becomeshigher than the set signal Vcons, so that, the voltage regulation canonce again be carried out correctly. Therefore, the first control signalSC1 once again moves to the low logic level, whereas the second controlsignal SC2 remains at the low logic level because the output currentIout has not always been exceeded. The output control signal SC thenmoves to the low logic level, which opens the switch formed by thetransistor T5. The output voltage Vout is therefore once again generatedand regulated at the target signal level Vcons.

Between the instants t2 and t3, the output current Iout becomes greaterthan a threshold Iout_max defined by the relationIout_max=(K*Iref*R1/R2). This exceeding of the output current Iout isdetected by means of the second control means COMP2 which then deliversa second control signal SC2 at a high logic level. The output controlsignal SC then moves to the high logic level, which closes the switchformed by the transistor T5. The output voltage Vout is then deactivatedand its level moves to zero. The first control signal SC1 remains at thelow logic level, because during this period no drop of the input voltageVup occurs.

Beyond the instant t3, the output current Iout once again becomes lowerthan the threshold current Iout_max, so that the power supply can onceagain be carried out without the risk of damaging the smart card. Thesecond control signal SC2 once again moves to the low logic level,whereas the first control signal SC1 remains at the low logic level. Theoutput voltage Vout is therefore once again generated and regulated atthe target signal level Vcons.

The system according to the invention can be advantageously used in aninterface circuit so that an output voltage Vout is generated to a smartcard. In particular, the interface circuit can be implemented in a smartcard reader.

The system according to the invention can also be used in an integratedcircuit intended to communicate with a smart card and in particularintended to generate an output voltage Vout to a smart card from aninput voltage Vup.

1. A system for generating an output voltage from an input voltages,said system comprising: regulation means for regulating said outputvoltage to a target voltage level, said regulation means comprising acontrol terminal that receives a regulation signal and an outputterminal for delivering said output voltage; first control means fordelivering a first control signal from a comparison between saidregulation signal and a first reference signal, the first control signalforming an indication that the regulation signal is outside a normalrange; and second control means for delivering a second control signalfrom a comparison between a fraction of the current delivered by saidregulation means on said output terminal and a second reference signal,the second control signal forming an indication that an output currentis outside a normal range.
 2. A system as claimed in claim 1 comprisingmeans for deactivating the generation of said output voltage from saidfirst control signal and/or said second control signal.
 3. An interfacecircuit comprising a system as claimed in claim 1 for generating saidoutput signal to a smart card.
 4. A smart card reader comprising aninterface circuit as claimed in claim
 3. 5. An integrated circuitcomprising a system as claimed in claim 1.